The Notch signalling pathway represents a critical component in the molecular circuits that control cell fate during development, cell survival and cell proliferation (Shih IeM, Wang T L in Cancer Res 2007; 67(5):1879-82). Aberrant activation of this pathway contributes to tumorigenesis. The Notch family members are being revealed as oncogenes in an ever-increasing number of cancers. The role of Notch in human cancer has been highlighted recently by the presence of activating mutations and amplification of Notch genes in human cancer and by the demonstration that genes in the Notch signalling pathway could be potential therapeutic targets. It has become clear that one of the major therapeutic targets in the Notch pathway are the Notch receptors, in which γ-secretase inhibitors prevent the generation of the oncogenic (intracellular) domain of Notch molecules and suppress the Notch activity.
Though significant progress has been made in dissecting the complex workings of this signalling pathway, there are very limited options available for Notch inhibitors. However, the pioneering class of Notch inhibitors is already in clinical trials for few cancer types, such as γ-secretase inhibitors MK0752 of Merck Sharp & Dohme Corp. MK0752, and RO4929097 (Roche), a synthetic small molecule, inhibits the Notch signalling pathway, which may result in induction of growth arrest and apoptosis in tumor cells in which the Notch signalling pathway is overactivated.
One of the drawbacks of use of γ-secretase inhibitors to block Notch signaling, as currently on the market or uner investigation, is their wide range of additional targets such as amyloid precursor protein as well as non-selectivity in blocking Notch signalling via all four ligands (Notch1, 2,3 and 4). Due to their ability to block Notch signalling via all four receptors γ-secretase inhibitors are known to cause goblet cell metaplasia in the intestine. In addition, some of the hematological malignancies and solid tumors harbor mutations in the Notch receptors (such as chromosomal translocations) resulting in constitutive expression of dominant active form of NICD independent of cleavage by γ-secretase complex. Therefore these tumors fail to respond to γ-secretase inhibitors treatment.
Therefore, there is still a need to identify and develop further specific and selective inhibitors of Notch signalling pathway useful for treating and/or preventing cancers.